Panicking

✅ Open the nrf52-code/radio-app/src/bin/panic.rs file and click the “Run” button (or run with cargo run --bin panic).

This program attempts to index an array beyond its length and this results in a panic.

$ cargo run --bin panic
   Compiling radio_app v0.0.0 (/Users/jonathan/Documents/ferrous-systems/rust-exercises/nrf52-code/radio-app)
    Finished `dev` profile [optimized + debuginfo] target(s) in 0.03s
     Running `probe-rs run --chip=nRF52840_xxAA --allow-erase-all --log-format=oneline target/thumbv7em-none-eabihf/debug/panic`
      Erasing ✔ 100% [####################]  12.00 KiB @  18.71 KiB/s (took 1s)
  Programming ✔ 100% [####################]  12.00 KiB @  14.22 KiB/s (took 1s)
  Finished in 1.49s
00:00:00.000000 [ERROR] panicked at src/bin/panic.rs:30:13:
index out of bounds: the len is 3 but the index is 3 (radio_app src/lib.rs:8)
`dk::fail()` called; exiting ...
Frame 0: syscall1 @ 0x00000cac inline
       /Users/jonathan/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/cortex-m-semihosting-0.5.0/src/lib.rs:201:13
Frame 1: report_exception @ 0x0000000000000caa inline
       /Users/jonathan/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/cortex-m-semihosting-0.5.0/src/macros.rs:28:9
Frame 2: exit @ 0x0000000000000caa
       /Users/jonathan/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/cortex-m-semihosting-0.5.0/src/debug.rs:74:25
Frame 3: fail @ 0x0000043e
       /Users/jonathan/Documents/ferrous-systems/rust-exercises/nrf52-code/boards/dk/src/lib.rs:456:9
Frame 4: <unknown function @ 0x000c0a36> @ 0x000c0a36

In no_std programs the behavior of panic is defined using the #[panic_handler] attribute. In the example, the panic handler is defined in the radio-app/lib.rs file, but we can change it:

✅ Change radio-app/lib.rs and change the panic panic handler, like:

#[panic_handler]
fn panic(info: &core::panic::PanicInfo) -> ! {
    defmt::error!("Oops!! {}", defmt::Debug2Format(info));
    dk::fail();
}

Now run the program again. Try again, but without printing the info variable. We purposely used the Display and Debug implementation of PanicInfo. What happens when you print info without defmt::Display2Format(..) or defmt::Debug2Format(..) wrapped around it?